This delightful church owes its Turkish name, "Little Saint Sophia", to its resemblance to Saint Sophia. Begun by Justinian in 527, the church of Saint Serge and Saint Bacchus was one of the largest Byzantine churches before it was converted into a mosque in the 16C. It is a stunning architectural example of an era of immense innovation: an irregular octagonal layout, crowned by a cupola divided into sixteen sections, set in a quadrilateral that served as a deambulatory.